As a method widely used in automatic analysis for blood, absorption photometry is known. In the absorption photometry, light is irradiated to a reaction solution prepared by mixing a biological sample with a reagent in a reaction container, an absorbance which is the attenuation of light having a specific wavelength is measured, and a concentration of a component of an analysis object is calculated from a relationship between the absorbance and the concentration. In many cases, a direct (linear) proportional relationship is established between the concentration and the absorbance of the component.
In the absorption photometry, as a technique of reducing influence of the noise caused by air bubbles or others in the reaction container on an analysis result, it is known to measure an absorbance of a sub wavelength in addition to the absorbance having the specific wavelength and calculate the concentration by using a difference between both absorbances or a ratio therebetween.
Moreover, in the absorption photometry, as a method used particularly for analyzing a minor component, a method of measuring the component based on light absorption due to aggregation substances such as latex agglutination and immunonephelometry is known. For example, in the immunonephelometry, a degree of aggregation of particles of an immune complex formed of a specific component and an antibody whose antigen is the specific component is analyzed by measuring an absorbance, so that the concentration of the specific component is calculated. In the latex agglutination, with using a reagent containing latex particles coated with antibodies directed to a specific component, a degree of aggregation of the latex particles is analyzed by measuring an absorbance, so that the concentration of the specific component is calculated.
Also in these methods, the influence of the noise can be often reduced by using the difference between the absorbances measured at two wavelengths or the ratio therebetween. However, in this case, a range where the concentration and the absorbance of the component are on the linear relationship is small. Therefore, in order to measure a concentration in a wide range, appropriate particle size, concentration, and wavelength are selected, and, for example, a spline function is used for a calibration curve instead of a straight line.
Patent Document 1 proposes a method in which, in order to reduce an analysis cost in the immunonephelometry, calibration curves having linear relationships at a plurality of wavelengths are previously obtained, and the calibration curves are switched depending on the concentration so that the shortest wavelength not causing the prozone effect is selected. According to the method, there is an effect that a linear calibration curve can be used even in the immunonephelometry.
Patent Document 2 proposes a technique in which, in order to reduce the influence of the noise, a plurality of items are measured at the same time by using measurement values of absorbances at three or more wavelengths. According to the technique, influence of a noise component having a wavelength dependency such as a serum color on an analysis result or others can be prevented.
Patent Document 3 proposes a technique in which, in order to improve the measurement accuracy in the latex agglutination, change from an absorbance at a reference measurement point to an absorbance at a measurement point within a range of a threshold value is obtained by the least square method. According to the technique, highly accurate measurement can be achieved even when an absorbance of a sample cannot be measured.